1. Field of the Invention
The invention relates to a method and to a series of devices for dry cleaning, activation, coating, modification, and biological decontamination (such as degerming, disinfection, sterilization) of surfaces by means of an atmospheric pressure plasma produced by means of so-called surface barrier discharge.
2. Description of the Related Art
Plasma technology methods can already be used, in standard manner, for treating material surfaces with the goal of cleaning (i.e. decontaminating), activating, functionalizing or coating the surface, in order to prepare it for subsequent technological processes, such as gluing, printing, varnishing, or to be able to carry work out under germ-free conditions. In the past, low-pressure plasmas were primarily used for this, particularly for complex surface geometries. Due to the high system costs for the vacuum apparatuses required for this, the discontinuous method of operation, as well as because the dimensions of the work pieces to be treated are restricted by the size of the recipient used, use of low-pressure plasma methods for large-scale technical applications is only possible with restrictions, particularly in industrial line production. Atmospheric pressure plasmas are used for integrating plasma technology methods of surface treatment into industrial production lines. Plasmas of this type can be produced, for example, by means of corona discharge or barrier discharge. However, they can also be used in the form of normal pressure jet plasmas that are generated on the basis of corona discharge, barrier discharge, or arc discharge, by means of implementing suitable process gas streams.
Methods and devices for surface treatment that are based on the use of such plasmas are described in numerous journals and, in part, also already used for different applications. However, the technical solutions described in these documents are connected with at least one or more of the following disadvantages:                Complicated, expensive power supply devices are needed.        Relatively high operating costs result from high energy consumption and, in part, also from a high gas consumption and from required cooling.        Uniform treatment (particularly coating) of the material is made difficult by the non-homogeneous structure of the plasmas.        In many cases, the discharges are non-homogeneous and consist of many small, energy-rich micro-discharges, which can lead to local material damage.        The devices cannot be used universally for simply any work pieces. Either they are suitable only for treatment of planar materials having a material thickness restricted to a few millimeters (such as foils and web materials, for example), or they can only be adapted to work pieces having a complex geometry by means of complicated positioning systems.        The devices cannot be used as manual devices for manually guided operation.        
The documents listed below also belong to the state of the art. In DE 195 32 412 A1, a method for surface pre-treatment of work pieces by means of a plasma jet is described, whereby the plasma jet is at first generated in a nozzle with electrodes, as an arc, and transferred onto the work piece to be treated, out of the electrode array, by means of a swirled working gas stream. In DE 298 05 999 U1, a device is described that carries a plasma jet directed parallel to the axis of rotation, by means of a rotation head having at least one eccentrically disposed plasma nozzle, as described above, and can plasma-treat surfaces. DE 10 2004 033 728 A1 describes a method for processing and gluing work pieces made of metal or a metal alloy having a hydrated oxide and/or hydroxide layer, whereby cleaning, activation, and subsequent treatment take place using an atmospheric plasma jet. DE 199 27 557 A1 describes a method for pre-treatment of work pieces to be welded or soldered, whereby a high-frequency arc discharge is provided between an electrode and the surface of the work piece to be treated. The device and method described here demonstrate significant differences from the methods and devices according to the invention described later. The electrode array is always structured in such a manner that the electrodes are situated on or in the immediate vicinity of the work pieces, and the plasma is produced directly at its location of effect, if possible. The gas stream used does not have the function of carrying the plasma out of the electrode array to the work piece, or to cool the electrode array, as in the case of the plasma jets, but rather merely serves for local intensification of the plasma at its location of effect and for control of its parameters (including the type and condition of the excited species). Because of the special electrode array, the gas consumption is kept very low, and the ignition voltage required for plasma operation is minimized. Thus, the required power supply devices can be structured to be very small, simple, and compact.
In DE 43 25 939 C1, WO 2004/053185 A1, and DE 38 27 629 A1, methods and devices for surface treatment are described, which are based on so-called volume barrier discharge (also called silent discharge, dielectrically inhibited discharge, or corona treatment). Experience has shown that the usability of so-called corona discharge systems is practicable only for the treatment of planar materials having a material thickness of a few millimeters (for example foils and web materials). In WO 2004/053185 A1, an electrode covered by a dielectric is used, in order to produce plasma in a reactive gas stream, in order to preserve metal surfaces, which function as a counter-electrode at the same time, by means of the plasma treatment. DE 38 27 629 A1 presents a method for surface pre-treatment of electrically conductive shaped materials, such as metal foil webs or plastic films into the polymatrix of which electrically conductive particles are embedded. The discharge is produced between discharge electrodes mantled by dielectric material and the metal core of a roller that serves as a grounded counter-electrode, whereby the foil web to be treated is transported over the roller. In addition, the working gas can be provided with an aerosol capable of being suspended in air, by means of an atomization device. In both cases, the counter-electrode and the discharge electrodes mantled by dielectric material form a discharge gap, so that so-called cold plasma is produced in the volume. In two of the aforementioned patents (DE 43 25 939 C1, WO 2004/053185 A1), so-called indirect corona treatments are also described. The corona nozzle presented in DE 43 25 939 C1 serves for indirect plasma treatment of web-form or profiled materials, and has at least two high-voltage electrodes between which an air stream that is guided to oscillate or circulate exits. In WO 2004/053185 A1, a so-called indirect barrier discharge is described for preserving metal surfaces. In both cases, the gas stream has the task, similar to a plasma jet, of driving the discharge out of the space between the two electrodes and onto the work piece to be treated. The gas stream thus acts on the shape and surface structure of the plasma. Three versions of the rotating or circulating guidance of the air stream are described.
In DE 102 19 197 C1, a method and a device for treating the surface of a metal wire, particularly as a coating pre-treatment, are described. In this connection, an alternating high voltage is applied to a metal wire on an electrode that is provided with a dielectric shield in the direction of the metal wire, in order to bring about a volume barrier discharge in the gas chamber, over the surface of the metal wire.